Big Aphid Hatch this Year

Aphids Are Flying

LOGAN, UT – The tiny bugs that have been flying gently in the breeze around faces and fruit trees are aphids. Starting the last week of September, they started swarming from the mid-section of Utah to Brigham City and areas north.

The Utah Plant Pest Diagnostic Laboratory at Utah State University has identified a variety of migratory aphid species this fall, including sunflower aphid, bird cherry-oat aphid, leafcurl plum aphid, mealy plum aphid and green peach aphid.

According to Marion Murray, USU Extension IPM project leader, these aphids are searching for an appropriate host to lay their eggs on so they will survive the winter.

“The aphid life cycle is rather interesting and complex,” she said. “Some species are migratory and need multiple plant hosts to complete their life cycle. The green peach aphid, for example, starts off in spring as eggs on peaches, nectarines, apricots and plums. The aphids feed on the foliage of these hosts all spring, and by late June, they leave the trees to feed on the foliage of vegetable plants and weeds.”

The length of the day and average temperatures signal the aphids to form wings and fly back to their woody hosts. They find their preferred tree in the fall through what is called “trivial flight,” where they fly at about 4 to 6 feet off the ground and move just a few feet at a time from leaf to leaf. The aphid then samples sap to see if it is the proper host. If not, it will continue on its trivial flight, land a few feet away and sample another host plant to see if it is the proper host.

Why are there so many this fall? Murray said one reason is the unseasonably warm temperatures over the summer and through September. This allowed the aphid populations to build to higher-than-average numbers. In addition, low level jet winds from southern Utah and Arizona can carry thousands of insects for hundreds of miles.

Murray said the swarms will not last. The first heavy frost will kill the aphids (but not their eggs), and until then, the oncoming temperatures of 40 F and below will cause feeding and flight to drop off dramatically.

“In the meantime, they are just a nuisance and should not be a cause for concern,” she said. “Research has shown that a high number of aphids in the fall does not correlate to a high number of aphids in the spring. To deal with aphids, it is best to wait until the spring and apply a dormant oil spray during bud swell.”